[USRP-users] TX and RX paths sharing a coherent LO

Rickard Radio rickardradio at gmail.com
Wed Oct 8 17:44:41 EDT 2014


OK, interesting.

Is it the exact same situation with two (or more) different transmitters
like TX1-TX2 as you explained here with TX-RX, namely that each path always
have physically different LO's but they are generated from the same 10MHz
reference?
Or can TX1-TX2 (or RX1-RX2) indeed use physically the same LO (i.e. with
same phase noise)?  Or is that impossible too?

That is, is there any difference with synched TX-RX compared to synched
TX1-TX2 (or RX1-RX2)?

The thing is that in my experiment I preferably would like to use
physically the same LO for all RX's and TX's (i.e., with exactly the same
frequency and jitter etc.) but perhaps I need to resort to synched, but
still ever so slightly different, LO's for each path.

Regards,
Rickard

On Wed, Oct 8, 2014 at 7:19 PM, Marcus Müller <usrp-users at lists.ettus.com>
wrote:

>  No, the LOs used for mixing are individually generated from the same
> 10MHz reference; they thus don't drift away from each other, but they don't
> share the same jitter etc. However, the Ettus daughterboards usually use
> rather decent synths, and thus the LO quality should be dominated by the
> quality of the reference clock -- which again, is quite ok, for most
> applications, and can be further optimized by GPS-disciplining the
> reference.
>
> Usually, that's how close you can get to shared LO if you want independent
> TX and RX mixers.
>
> Greetings,
> Marcus
>
>
> On 08.10.2014 19:04, Rickard Radio via USRP-users wrote:
>
> Sounds good!
>
> Does this mean it really shares the same LO, i.e., also with the same and
> uniquely occurring phase noise shared to all paths?! (I want that!)
>
> Regards,
> Rickard
>
>
>
> On Wed, Oct 8, 2014 at 6:54 PM, Marcus Müller <usrp-users at lists.ettus.com> <usrp-users at lists.ettus.com>
> wrote:
>
>
>   Hi Rickard,
>
> all the LOs are synthesized from the same motherboard reference, so Q1 is
> answered with "you get that for free".
> Q2 is "yes".
> Q3 gets the answer "if you want to use definite times when sampling, use
> the timed commands feature of UHD".
> :)
>
> Greetings,
> Marcus
>
> On 08.10.2014 18:48, Rickard Radio via USRP-users wrote:
>
> Dear usrp-users,
>
> I am interested in coherently LO-mixing different TX and RX paths for some
> experiments.
>
> Q1: Which options exist to use the same(?) coherent(!) LO for different TX
> and RX paths on the USRPs (N210 and/or B210)?
> Q2: Related, with the N210s and the MIMO cable, can I obtain and use a
> coherently shared LO for different TX and RX paths?
> Q3: Follow up  - do I need something else or in addition ?
>
> Regards,
> Rickard
>
>
>
>
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